Development of cementitious materials from the magnesium silicate minerals. (2020)
Type of ContentTheses / Dissertations
Thesis DisciplineCivil Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
Concrete is the second most-consumed items in the world after water. Although cement only accounts for 10-20% of the concrete's weight, it attributes up to 95% of the total carbon emission. Because of the large amount consumed every year, it emitted around 8% of the total carbon emission. Many solutions were proposed or already in place to reduce the carbon footprint during the manufacturing, design, use and end of life stages. Among these initiatives, using MgO-based cement is one of the most promising approaches. However, the availability of the MgO is limited compared to the raw material to prepare Portland cement. Especially in New Zealand, there is no production for MgO, thus it has to be imported from overseas. On the other hand, New Zealand is rich in magnesium-rich silicates rocks, such as olivine and serpentine. Therefore, this research conducted a feasibility study on the magnesia and silica extraction from these magnesium silicates minerals and then used them as a binder system.
The dissolution properties of the olivine under different conditions were first investigated. It was highlighted that the dissolution rate was in a good relationship with the pH value, and mechanical grinding also improved its dissolution rate. As a result, acid digestion was proposed to process the fine mineral particles. The magnesia (MgO) was successfully recovered from the olivine after digestion, separation, evaporation and thermal decomposition. However, it was identified that the recovered products only contained 52.1% MgO while the SiO₂ impurity took up 27.9%. The reactivity of the recovered MgO is lower than MgO from a commercial source. In terms of silica(SiO₂) extraction, acid digestion was also used on serpentine. To systematically investigate the reactivity of the recovered silica, seven different characterisation techniques were used and compared with other silica sources. It concluded that the recovered silica contains a certain proportion of amorphous silica phase, and it was pozzolanic active.
The recovered MgO was then mixed with the extracted SiO₂. The sample mixed with recovered products demonstrated higher strength than it mixed with commercial MgO and silica fume. It was also noted that the strength of the sample containing recovered MgO was constantly higher than it with commercial MgO source. This was caused by the presence of amorphous silica in the recovered MgO. The amorphous silica reacted with the MgO and formed the magnesium silicate hydrate gel, contributing to the strength gain. However, the recovered silica did not show any comparable reactivity to the silica fume.
Lastly, since hydrochloride acid (HCl) was used for acid digestion, it generates a considerable amount of waste acid. The magnesia was then proposed to neutralise the waste acid and to develop the MgO-HCl binder system. The mix of MgO with waste acid showed superior mechanical properties, especially at early ages. It reached more than 40 MPa at 3 days which was more than doubled of the mix with MgO+H₂O. The hydration products of the MgO +waste acid were found to be brucite, magnesium carbonates and 3MgO-MgCl₂- 8H₂O (phase 3). These products were similar to the Sorel cement/magnesium oxychloride cement.
To conclude, this research proved the feasibility of extracting magnesia and silica from ultramafic minerals and developed the prototypes of the MgO+SiO₂+H₂O and MgO- HCl binder systems.
RightsAll Right Reserved
Showing items related by title, author, creator and subject.
Sarpong B; Shah V; Scott A; Watson, Matthew (Engineers Australia Pty. Ltd., 2020)Magnesium oxide (MgO) has a wide range of applications in civil engineering, agriculture, paint, and medicine. It can be used to produce refractory bricks, cement, and insulators for fire-resistant cables. In medicine, MgO ...
Scott A; Oze C; Shah V; Yang N; Shanks B; Cheeseman C; Marshall A; Watson M (2021)Global climate change related to anthropogenic CO2 emissions is one of the most significant challenges for the future of human life on Earth. There are many potential options for reducing or even eliminating atmospheric ...
Tran, Hung (University of Canterbury, 2019)Studies on magnesium-based cement have been of interest to mitigate the increasing impact of climate change due to the high CO2 emissions associated with cement production industry. Although magnesium silicate hydrate ...